Mass Spectrometric Study of Photoionization V. Water and Ammonia.

Photoionization efficiency curves are obtained for the molecule and fragment ions of H2O and NH3 in the wavelength region extending from onset of ionization to 600 Å. Threshold values of 12.593 eV and 10.162 eV are observed for the H2O+ and NH 3 + ions, respectively. Vibrationally excited states of the molecule ions and autoionization of Rydberg levels are observed. A determination of the bond angle of the H2O+ ion from the Franck-Condon factors of the bending overtones results in a value of 112 degrees. Threshold values of the fragment ions permit calculations of heats of formation of the OH+ and NH 2 + ions and result in the ionization energies, I ( OH ) = 12.94 eV and I ( NH 2 ) = 11.22 eV . .